SK154797A3 - Process for producing caprolactam - Google Patents

Abstract

The production of caprolactam by reacting 6-amino capronitrile with water in the presence of catalysts, using an initial mixture of 6-amino capronitrile and the tetrahydroazepine derivative of formula (I), and reaction in the liquid phase in the presence of heterogeneous catalysts, and a process for producing tetrahydroazepine derivative (I) and its use for making caprolactam and polycaprolactam.

Description

Field: techniques

The present invention relates to a process for preparing caprolactam by reacting 6-aminocapronitrile with water in the presence of a catalyst.

BACKGROUND OF THE INVENTION

Heating of 6-aminocapronitrile, but also at room temperature, for example during long-term storage of 6-aminocapronitrile, yields a brown tetrahydroazepine derivative (THA derivative I) of the formula I

N (H) - (CH ₂ ) ₅ CN (I)

The THA derivative also includes the tautomeric form

N- _(CH2) 5CN

EP-A 497 333 describes direct polymerization of caprolactam starting from 6-aminocapronitrile.

A solved problem of this described process is the removal of tetrahydroazepine (THA) prior to the polymerization operation, since tetrahydroazepine leads to an undesirable coloration of the polymers that occurs by polymerization of caprolactam in the presence of tetrahydroazepine. Said patent discloses treatment with a basic compound such as an alkali metal hydroxide or an alkali metal oxide as a solution. After work-up, the 6-aminocapronitrile can conveniently be separated from the reaction mixture, which is not possible without proper work-up.

EP-A 502 439 addresses the problem of removal of THA in the presence of 6-aminocapronitrile by treatment with sodium borohydride. Also in this case, after the processing operation, 6-aminocapronitrile can be separated very well from the reaction mixture by distillation.

DE-AS 25 42 396 and 25 42 397 disclose the reaction of gamma-aminobutyronitrile to a mixture comprising 2- (N-gamma-cyanopropyl Jamino-delta-4-pyroline (CAP) and 2-amino-delta- ^1- pyrroline ( AP) and further hydrolysis of the isolated CAP to pyrrolidone-2 in the absence of a catalyst Both DE publications disclose in no way whether the corresponding THA derivative I can be reacted similarly in the presence of heterogeneous liquid phase catalysts to caprolactam. DE-AS isolates CAP as a pure substance prior to hydrolysis of CAP, therefore it would be expected that the use of mixtures containing THA derivative I would lead to a greater degree of unwanted intermediates. Seven (Rómpp Chemie Lexikon 9th Edition, Falbe and Regitz, Georg Thieme Publishing, New York) Based on experience with THA, one would expect That is, the THA derivative I would result in colored polycaprolactam both in the cyclization of 6-aminocapronitrile to polycaprolactam and in the direct reaction of 6-aminocapronitrile to polycaprolactam if it did not separate prior to cyclization and before the polymerization operation.

Furthermore, it has to be assumed that the THA derivative I reduces the useful life of the catalyst used in the polymerization, as U.S. Pat. No. 5,162,567 discloses that high-boiling substances, i.e. higher boiling substances or mixtures, are formed when heating THA. such as 6-aminocapronitrile (and 6-aminocapronitrile can also be separated accordingly). However, the high-boiling substances tend to form polymeric or oligomeric degradation products which can deposit on the surface of the catalyst and thus reduce both the life and activity of the catalysts used.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a process for cyclizing 6-aminocapronitrile to caprolactam, in which the THA derivative I does not reduce the life or activity of the catalyst used in the cyclization and leads to a caprolactam-containing reaction mixture. Preferably, the UV characteristic, depending on the content of THA derivative I, after cyclization, should be less than before the cyclization operation. In addition, in the direct polymerization of 6-aminocapronitrile, the THA derivative I contained in the reaction mixture or the reaction mixture should either be readily separated or the reaction conditions should be chosen such that the THA derivative I is eliminated.

SUMMARY OF THE INVENTION

The process for preparing caprolactam by reacting 6-aminocapronitrile with water in the presence of catalysts, according to the invention, consists in using a starting mixture consisting of 6-aminocapronitrile and a tetrahydroazepine derivative of formula I (I) and carrying out the reaction in liquid phase in the presence of heterogeneous catalysts.

The invention further relates to a tetrahydroazepine derivative of the formula I, a process for its preparation and the use of the THA derivative I for the production of caprolactam.

According to the invention, the reaction is carried out in the liquid phase in the presence of heterogeneous catalysts at temperatures generally 140 to 320 ° C, preferably at 160 to 280 ° C and a pressure of 0.1 to 25 MPa, preferably 0.5 to 15 MPa, taking into account for the reaction mixture to be liquid under the conditions used, i.e. without the solid phase catalyst. The reaction time is usually 1 to 120 minutes, preferably 1 to 90 minutes, and most preferably up to 60 minutes. In some cases, a reaction time of 1 to 10 minutes has been shown to be quite sufficient.

In general, at least 0.01 mol, preferably 0.1 to 20 mol and in particular 1 to 5 mol of water are used per mole of THA derivative I.

Preferably, the THA derivative I is used in the form of 1 to 50% by weight, preferably 5 to 50% and most preferably 5 to 30% of an aqueous solution (whereby water is simultaneously the reactant) or in water / solvent solution mixtures. Solvents which may be mentioned are, for example, alkanols such as methanol, ethanol, n-propanol and isopropanol, n-butanol, isobutanol, tert-butanol and polyols such as diethylene glycol and tetraethylene glycol, hydrocarbons such as petroleum ether, benzene, toluene, xylene, lactams such as pyrrolidone. or caprolatam or alkyl-substituted lactams, such as N-methylpyrrolidone, N-methylcaprolactam or N-ethylcaprolactam, as well as esters of a carboxylic acid, preferably a carboxylic acid having 1 to 8 carbon atoms. Ammonia may also be present in the reaction mixture. Of course, mixtures of organic solvents may also be used. Mixtures of water and alkanols in a water / alkanol weight ratio of 1 to 75 to 25 to 99, preferably 1 to 50 to 50 to 99, have proven to be particularly advantageous in individual cases.

The content of THA derivative I relative to the 6-aminocapronitrile in the starting mixture may be 0.01 to 95%, preferably 0.1 to 50%, and particularly preferably 0.5 to 20%.

Usually, the starting mixture shows, depending on the content of THA derivative I, a UV characteristic of 5 to 40,000 (reported as the sum of all extinctions measured on a 10% by weight solution in ethanol at wavelengths of 280 to 400 nm, based on a cuvette length of 5 cm).

The starting mixture is obtained by heating 6-aminocapronitrile with or without a solvent. According to the prior art, the temperature may be 20 to 280 ° C, preferably 50 to 250 ° C, particularly preferably 100 to 230 ° C. As expected, shorter reaction times at higher temperatures are possible. The reaction can be carried out at a pressure of 100 to 25 MPa, preferably at 500 to 20 MPa. It may further be advantageous to carry out the reaction in the presence of an acidic homogeneous or heterogeneous catalyst, such as a mineral, carboxylic or sulfonic acid, titanium dioxide, alumina, acidic ion exchangers or Lewis acids.

Optionally, the pure THA derivative I can be obtained, for example, by distillation of unreacted 6-aminocapronitrile, a solvent and optionally by-products.

The following may be used as heterogeneous catalysts: acidic, basic or amphoteric oxides of elements of the second, third or fourth main groups of the periodic system, such as calcium oxide, magnesium oxide, boron oxide, alumina, tin oxide or silica in the form of fumed silica , silica gel, diatomaceous earth, quartz or mixtures thereof, and metal oxides of the second to sixth subgroup of the periodic system, such as titanium dioxide, amorphous such as anatase and / or rutile, zirconia, zinc oxide, manganese oxide or mixtures thereof. Also useful are oxides of lanthanides and actinides such as cerium oxide, thorium oxide, prazodyne oxide, samarium oxide, rare earth mixed oxide or mixtures thereof with the above-mentioned oxides. Other catalysts may be, for example, vanadium oxide, niobium oxide, iron oxide, chromium oxide, molybdenum oxide, tungsten oxide or mixtures thereof. Mixtures of the above oxides with each other are also useful. Sulfides, selenium and tellurides such as zinc telluride, tin selenide, molybdenum sulfide, tungsten sulfide, nickel, zinc and chromium sulfides are also useful.

Said compounds may be enriched with or contain optionally compounds of the main groups of the Periodic System.

In addition, zeolites, phosphates and heterogeneous polyacids as well as acidic and alkaline ion exchangers such as Naphion ^R may be mentioned as suitable catalysts.

The catalysts may optionally contain up to 50% by weight of copper, tin, zinc, manganese, iron, cobalt, nickel, ruthenium, palladium, platinum, silver or rod.

Depending on their composition, the catalysts may be used as such or supported. Thus, for example, titanium dioxide may be deposited in a thin titanium dioxide layer on a support, such as or zirconium oxide, with a layer of oxide on the support in the literature. For the deposition of the oxide is silica, alumina can be used by all the methods described. Thus, titanium dioxide can be formed by hydrolysis of organic titanium compounds, such as titanium isopropylate or titanium butlate, or by hydrolysis of titanium tetrachloride or other inorganic compounds. Also useful are salts containing titanium dioxide.

Particularly preferred are catalysts which do not contain components soluble under the reaction conditions.

In another preferred embodiment of the invention, the reaction is carried out in a fixed bed reactor. In the fixed bed method, tablets or sticks having a diameter of 1 to 10 mm are used. In principle, however, the reaction can also be carried out in a suspension manner.

In a further preferred embodiment, in particular, heterogeneous catalysts based on titanium dioxide, zirconia, cerium oxide and aluminum oxide are used.

Aluminum oxide is suitable in all modifications obtained by heating aluminum hydroxide as a precursor (gibbsit, boehmite, pseudo-boehmite, bayerite and diaspore) at various temperatures. These include in particular gamma-alumina and alpha-alumina and mixtures thereof.

The oxides may be used in pure form (content of individual oxides by weight> 80%), as a mixture of the said oxides, the sum of the abovementioned oxides being by weight> 80%, or as a supported catalyst in which the above oxides are applied mechanically; chemically stable carrier, mostly over a large area.

Pure oxides can be obtained by precipitation from aqueous solutions, for example titanium dioxide or sulfate, or by other methods such as the pyrogenic production of fine alumina, titanium dioxide or zirconium dioxide powders, which are commercially available.

Various methods can be chosen for the production of mixtures of different oxides. The oxides or their precursors, which can be converted into oxides by calcination, can be produced, for example, by co-precipitation from solutions. In this case, a very good distribution of the two usable oxides is generally achieved. The oxides or premixes can also be obtained by precipitation of one oxide or precursor in the presence of a suspension of finely divided particles of the other oxide or precursor. Another method consists in mechanically mixing the powder of the oxide or precursor, which mixture can be used as a starting material for the production of bars or tablets.

The supported catalysts can be produced in various ways. For example, titanium dioxide can be applied in the form of a sol by simply impregnating it onto a support. By drying and calcining, the volatile components of the sol are usually removed. Such soles are commercially available for titanium dioxide, alumina and zirconia.

Another possibility of deposition of active titanium dioxide layers is the hydrolysis or pyrolysis of organic or inorganic compounds. Thus, for example, a ceramic support can be coated in a thin layer with titanium dioxide by hydrolysis of titanium isopropylate or other titanium alkoxides. Other preferred compounds are, for example, titanium tetrachloride, zirconium chloride, aluminum nitrate and cerium nitrate. Suitable carriers are powders, sticks or tablets of said oxides themselves or other stabilized oxides such as silica. The carriers used may be macroporous to facilitate substance transfer.

According to a further particularly preferred embodiment of the invention, titanium dioxide is used as the catalyst with anatase content of 100 to 5%, preferably 99 to 10% and a rutile content of 0 to 95%, preferably 1 to 90%, based on the total titanium dioxide content.

The THA derivative I is preferably used for the production of caprolactam by reacting the THA derivative I with water / solvent at a temperature of 140 to 320 ° C, preferably 160 to 280 ° C and at a pressure of 100 to 2500 kPa, in particular 500 to 500 kPa. 2000 kPa, in the presence of the above heterogeneous catalysts, preferably containing titanium dioxide, similar to the aforementioned starting mixture, wherein the molar ratio of THA derivative I to water is chosen from 0.01 to 20, preferably 0.5 to 20.

The aforementioned starting mixture in the form of an aqueous solution or as the THA derivative I itself can be converted by heating to polycaprolactam by known methods, for example as described in EP-A 150 295.

An advantage of the process according to the invention is that a process has been found in which reaction mixtures containing a THA derivative can be

Even with 6-aminocapronitrile lactam, or, in the case of products obtained, or without difficulty, to be converted into cap-needs for polycaprolactam. Thus, their mixtures no longer contain the interfering THA derivative I. Further processing operations and the addition of additional reagents as compared to the removal of THA from the respective reaction mixtures are no longer required.

In certain circumstances, it may even be advantageous to convert the 6-aminocapronitrile by preheating to 20 to 280 ° C in whole or in part to the THA derivative I and the mixture thus obtained.

THA-derivative I and 6-aminocapronitrile used for cyclization on oxide catalysts.

The invention is illustrated, but not limited, by the following examples. Percentages are by weight unless otherwise indicated.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

400 g of 6-aminocapronitrile are held at 200 ° C for 8 hours. By distillation, the THA derivative I (yield 10% of theory) is obtained as a second compound at a pressure of 10 Pa at a temperature of 140 ° C. Characteristics by NMR spectroscopy:

¹ H-NMR (250 MHz, DMSO-d 6, TMS, ppm):

4.2 (s, broad, 1H), 3.2 (m, 2H), 2.9 (t, 2H), 2.45 (t, 2H),

2.25 (m, 2H); 1.7-1.1 (m, 12H).

¹³ C-NMR (62.9 MHz, DMSO-d6, TMS, ppm):

163.3 s, 120.6 s, 47.0 t, 41.6t, 32.9 t, 30.6 t, 29.7 t, 28.4 t, 26.0 t, 25.6 t, 24 8 t, 16.2 t.

Example 2

A 10% ethanol solution of THA derivative I is pumped together with 2 moles of water (corresponding to 3.2% of the solution as a whole) at a rate of 70 ml / h through a tubular reactor (6 mm diameter, 800 mm length) filled with titanium dioxide. The reactor temperature is 230 ° C, pressure 8 MPa. Within 9.7 hours, a 9.7% ethanol caprolactam solution was obtained. The solution further contains 0.8% ethyl 6-aminocaproate which can be recycled into the solution as well as 0.2% 6-aminocaproic nitrile which can be recycled into the solution. The yield of caprolactam is 80% of theory, the selectivity, including the compounds that can be reintroduced into the process is 95%.

Example 3

A 10% ethanol solution containing 95% ACN and 5% THA derivative I is pumped together with 2 moles of water (corresponding to a tubular reactor (diameter 6 mm, length 800 mm) filled with titanium dioxide).

3.2% of the solution as a whole) at a rate of 70 ml / h. The reactor temperature is 230 ° C, pressure 8 MPa. Within an hour, a 9.1% ethanol solution of caprolactam was obtained. The solution further contains 0.4% 6-aminocaproic acid ethyl ester which can be recycled into the solution as well as 0.1% 6-aminocaproic acid nitrile which can be recycled into the solution. The yield of caprolactam is 91% of theory, the selectivity, including compounds that can be reintroduced into the process is 95%.

Example 4

A 10% ethanol solution was pumped together with 2 moles of water at a rate of 70 ml / h through a tubular reactor (6 mm diameter, 800 mm length) filled with titanium dioxide. Reaching 99% ACN and 1% THA derivative (corresponding to 3.2% of the solution as a whole) over an hour

The reactor temperature is 230 ° C, a pressure of 8 MPa obtains a 9.0% ethanolic caprolactam solution. The solution further contains 0.4% of 6-aminocaproic acid ethyl ester which can be recycled to the solution as well as 0.1% of 6-aminocaproic acid nitrile which can be recycled to the caprolactam is the solution. The yield, including the compounds, is 95%.

theory, selectivity, which can be reintroduced into the process

Industrial usability

A process for preparing caproclactam by reacting 6-aminocapronitrile with water in the presence of catalysts, using a mixture of 6-aminocapronitrile and a tetrahydroazepine derivative as the starting material, wherein the reaction is carried out in the liquid phase in the presence of heterogeneous catalysts.

Claims (11)

PATENT CLAIMS A process for preparing caprolactam by reacting 6-aminocapronitrile with water in the presence of catalysts, characterized in that a starting mixture consisting of 6-aminocapronitrile and a tetrahydroazepine derivative of the formula I 'N is used. N (H) - (CH ₂ ) ₅ CN (I) and the reaction is carried out in the liquid phase in the presence of heterogeneous catalysts. Process according to claim 1, characterized in that the heterogeneous catalysts do not contain components soluble under the reaction conditions. Process according to claim 1 or 2, characterized in that the reaction is carried out in a fixed bed reactor. The process according to claims 1 to 3, characterized in that the reaction is carried out in the presence of heterogeneous catalysts based on titanium dioxide, zirconia, cerium oxide and aluminum oxide. Process according to Claims 1 to 4, characterized in that titanium dioxide is used as the catalyst, containing by weight 5 to 100% of anatase and 0 to 95 rutile, based on the content of titanium dioxide as a whole. Method according to claims 1 to 5, characterized in that the starting mixture has a UV characteristic of 5 to 40 000, given as the sum of all extinctions measured on a 10% by weight solution in ethanol at wavelengths of 280 to 400 nm, relative to the length of cuvette 5. cm. A tetrahydroazepine derivative of the formula I ^N N (H) - (CH ₂ ) 5 CN _; ^(I) .. as an intermediate in the process for producing caprolactam according to claim 1. A process for the preparation of a tetrahydroazepine derivative of the formula I according to claim 7, characterized in that the 6-aminocapronitrile is heated at a temperature of 100 to 300 ° C. A tetrahydroazepine derivative of the formula I for the production of caprolactam and polycaprolactam. 10. A process for producing caprolactam, comprising reacting a tetrahydroazepine derivative of formula I with water at a temperature of 140 to 320 ° C and a pressure of 100 to 2500 kPa, wherein a molar ratio of the tetrahydroazepine derivative to water of 0.01 to 20 is selected. 11. A process for preparing caprolactam by heating an aqueous solution of 6-aminocapronitrile, wherein the aqueous solution comprises a tetrahydroazepine derivative of the formula I.